The process for producing cyclododecanones by isomerizing an epoxycyclododecane in the presence of a lithium halide catalyst is known from several reports.
For example, German Patent DE3744094 discloses a technique where an epoxycyclododecane is isomerized by using N-methylpyrrolidone or N,N′-dimethylethyleneurea as a solvent and using lithium chloride as a catalyst and thereby a cyclododecanone is obtained in a yield of 94%.
Also, German Patent DE3601380 discloses a technique where 1,2-epoxycyclododeca-5,9-diene is isomerized in the presence of sodium iodide in a polyethylene glycol solvent (NaI: 3 wt %, 195° C., 9 hours) and thereby cyclododeca-3,7-dien-1-one is produced in a yield of 98.7%.
In either one of these methods, a polar solvent is used and therefore, a step for recovering or decomposing the solvent must be added, but this causes a problem of increase in the production cost. Furthermore, in these methods, the isomerization rate is decreased due to dilution effect or solvation effect of the solvent and this causes a problem that, for example, the reaction apparatus is large. Thus, these methods are not favored with an industrially high efficiency.
USSR Patent SU407874 discloses a technique of isomerizing an epoxycyclododecane by using no solvent and using anhydrous LiBr as the catalyst. In Examples of this patent, the reaction is performed by using 4 wt % of LiBr at a reaction temperature of 120 to 130° C. for a reaction time of 18 hours or by using 3.3 wt % of LiBr at a reaction temperature of 200° C. for a reaction time of 3 hours and thereby, the cyclododecanone is obtained in a yield of 100% or 83.3%, respectively. In the former Example, the reaction time is long and in the later Example, the yield is low. Thus, the methods are not practical.
In this USSR method, it may be considered to enhance the reaction rate by increasing the catalyst concentration or elevating the reaction temperature. However, in the former Example, the solubility of the catalyst comprising LiBr is already saturated at that reaction temperature and therefore, the catalyst concentration cannot be increased. In the latter Example, the reaction temperature is elevated so as to enhance the reaction rate, but in this case, a side reaction proceeds and the yield of the objective compound greatly decreases.
Furthermore, Zh. Org. Khim, 26(7), 1497-1500 (1990) discloses that when an isomerization reaction of an epoxycyclododecane is performed by using no solvent and using lithium bromide as the catalyst under the conditions of 2.3 mol of LiBr, 150° C. and 10 hours, the cyclododecanone is obtained in a yield of 96.6%, and when the reaction is performed by using lithium iodide as the catalyst under the conditions of 1.5 mol % of LiI, 150° C. and 5 hours, the cyclododecanone is obtained in a yield of 91.2%. However, also in the methods of this publication, it is feared that a fairly long reaction time is necessary to achieve a conversion close to 100% of epoxycyclododecane.
As described above, conventional production processes of cyclododecanones through isomerization of epoxycyclododecanes have those problems and a production process of a cyclododecanone, which can be practiced in an industrial scale with high efficiency and high selectivity, is not yet found out.
One problem encountered in industrially practicing the process for producing a cyclododecanone by isomerizing an epoxycyclododecane is the difficult separation of the cyclododecanone as the objective compound from the epoxycyclododecane used as the starting material. More specifically, the boiling point of the epoxycyclododecane and the boiling point of the cyclododecanone as an isomerization reaction product thereof are close to each other and, therefore, when unreacted epoxycyclododecane remains in the reaction system, the separation and recovery of this compound from the cyclododecanone by distillation is very difficult. Furthermore, these two compounds analogize with each other in the physical properties (for example, crystallinity and solubility) and therefore, the separation and recovery of two compounds by crystallization or extraction is also difficult. Accordingly, when unreacted epoxycyclododecane remains in the reaction system, a high-purity cyclododecanone can be hardly recovered. At the same time, from the above-described reasons, the unreacted epoxycyclododecane can be hardly recovered and re-used by an ordinarily employed technique but a special recovery technique is necessary and this inevitably causes an increase in the production cost of the objective compound. Therefore, in order to stably produce a high-purity cyclododecanone in industry, it is necessary to constantly achieve a nearly 100% conversion of the epoxycyclododecane. For realizing this in industry, the reaction rate must be maintained in a high level.
However, as described above, conventional techniques fail to provide a level high enough for industrial practice. Furthermore, if the reaction temperature is elevated so as to enhance the reaction rate, a side reaction readily takes place to produce a high-boiling-point material or the like and this causes a problem of reduction in the selectivity to cyclododecanone. In order to solve this problem, it may be considered to elevate the catalyst concentration, but this is not practical because the solubility of catalyst is limited and furthermore, the catalyst cost increases.
The epoxycyclododecane used as a starting material in the process of the present invention can be industrially produced by subjecting a cyclododecatriene obtained through trimerization of butadiene to an appropriate combination of oxidation reaction and hydrogenation reaction. For example, an epoxycyclododecadiene obtained by epoxidizing a cyclododecatriene is subjected to reduction with hydrogen in the presence of a catalyst such as platinum, palladium or nickel, whereby the epoxycyclododecane can be obtained.
In the thus-obtained epoxycyclododecane, hydroxyl group-containing cyclododecane compounds such as cyclododecanol are contained as impurities, but the effect of such impurities on the isomerization of epoxycyclododecane has been heretofore not studied. That is, a technique capable of efficiently producing a cyclododecanone from a starting material containing such impurities, with high selectivity in an industrial scale is not known at present. Here, the epoxycyclododecane and the hydroxyl group-containing cyclododecane compound such as cyclododecanol can be separated by a general industrial method such as distillation.